Ionized gas and stellar kinematics have been measured along
the major axes of seventeen nearby spiral galaxies of intermediate to late
morphological type. We discuss the properties of each sample galaxy,
distinguishing between those characterized by regular or peculiar
kinematics. In most of the observed galaxies, ionized gas rotates
more rapidly than stars and has a lower velocity dispersion, as is to be
expected if the gas is confined in the disc and supported by rotation
while the stars are mostly supported by dynamical pressure. In a few
objects, gas and stars show almost the same rotational velocity and low
velocity dispersion, suggesting that their motion is dominated by
rotation.
Incorporating the spiral galaxies studied by Bertola et al. ([CITE]),
Corsini et al. ([CITE], [CITE]) and Vega Beltrán et al. ([CITE]) we have
compiled a sample of 50 S0/a-Scd galaxies, for which the major-axis
kinematics of the ionized gas and stars have been obtained with the same
spatial (≈) and spectral (≈50 ) resolution,
and measured with the same analysis techniques. This allowed us to
address the frequency of counter-rotation in spiral galaxies. It
turns out that less than and less than (at the confidence level) of the sample galaxies host a counter-rotating
gaseous and stellar disc, respectively. The comparison with S0 galaxies suggests that the retrograde acquisition of small amounts of
external gas gives rise to counter-rotating gaseous discs only in
gas-poor S0s, while in gas-rich spirals the newly acquired gas is
swept away by the pre-existing gas. Counter-rotating gaseous and
stellar discs in spirals are formed only from the retrograde
acquisition of large amounts of gas exceeding that of pre-existing
gas, and subsequent star formation, respectively.

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